"The National Bank of Ukraine has warned banks... About an external hacker attack on the websites of some Ukrainian banks... Which was carried out today," the bank said in a statement.
Banks were experiencing "difficulty in servicing customers and performing banking operations" due to the attacks, it said.
"All the financial market participants have taken steps to tighten security measures to counteract these hacker attacks," it said, adding that "banking infrastructure is securely protected" and further attacks "will be efficiently warded off."
"The bank's services together with the National Bank of Ukraine are putting in maximum effort to reinstate access to all bank services," it said.
Earlier an attack was also reported by the power company in Kiev, Kyivenergo. "We were forced to turn off all of our computers," a company representative told Interfax Ukraine agency.
Ukraine's delivery service company Nova Poshta, which was also attacked today, identified the virus that hit its computers as Petya.A, a type of ransomware which locks users out of the system and demands purchase of a key to reinstate access.
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